Reversible and Irreversible Dehydration of Hydroxy‐Interlayered Vermiculite from Coastal Plain Soils

Abstract

AbstractDehydration behavior of hydroxy‐interlayered vermiculite (HIV) from three coastal plain soils was studied using x‐ray diffraction (XRD) and thermal analysis. Relative humidity (RH) at 25 °C had little effect on HIV 001 XRD peaks, except for a 0.01 to 0.05° 2θ shift at RH ≈ 0%. Heating to 50 °C shifted peak positions 0.10 to 0.20° 2θ for fine silts and 0.05 to 0.10° 2θ for coarse clays. Effects of 50 °C treatment were largely reversed by re‐wetting, indicating that H2O re‐entered interlayers. Heating to 115 °C broadened peaks and produced shifts of up 0.40° 2θ. Dehydration at ≥ 115 °C was essentially irreversible, as indicated by lack of 001 expansion and failure to regain full sample weight at 100% RH. Peaks were markedly broadened and attenuated by heating to 165 and 225 °C, with full width at half maxima approaching 1.0° 2θ. No significant peak in the 1.0‐nm region developed from interlayer collapse, even at 550 °C. Reversible dehydration may be attributable to free‐H2O loss from interpolymer zones at temperatures below the onset of significant polymer dehydration. The data suggest that attraction between dehydrated polymers and 2:1‐layer surfaces exceeds hydration forces, resulting in irreversible collapse and variable interlayer thickness. Re‐entry of H2O into interlayers could be sterically impeded by the dehydrated polymers themselves or by their binding effect on layers. The 1.4‐nm mineral in the soils studied exhibits thermal properties more consistent with HIV than an alternative vermiculite‐kaolin intergradient structure.